To date, several telecommunication systems have been proposed for carrying signals for different types of communication applications in the same signal stream. Some of these systems integrate signals for narrowband applications (e.g., telephony signals) with signals for broadband applications (e.g., video and data signals) in the signal streams that they transmit. For systems that transmit integrated signal streams in a cell based format, the signal stream can contain a mixture of cells having asynchronous application signals (i.e., signals for asynchronous communication applications) and cells having isochronous application signals (i.e., signals for isochronous applications).
Integrated telecommunication systems, that carry different types of signals for different types of applications, have to properly multiplex and demultiplex the different signals in the signal stream. For instance, some integrated broadband/narrowband systems have to separate the isochronous application signals (e.g., such as telephony signals) from the asynchronous application signals (e.g., video and data signals). A simple prior art method for extracting isochronous telephony signals reads all of the bytes in a received frame into a memory and subsequently determines the isochronous bytes.
FIGS. 1 and 2 set forth one implementation of this prior art technique. As shown in FIG. 1, the prior art includes a memory 105 which sequentially stores every byte of a received frame in contiguous byte-wide memory locations. This prior art implementation also includes a table of pointers 110 with a pointer for each memory location. Each pointer for a memory location that stores telephony bytes points to a specific twisted pair 210 of a specific telephone-interface-unit (TIU) card 205, as set forth in FIG. 2. Hence, once the memory completely stores all bytes of a received frame, the isochronous telephony bytes in the memory are routed to the appropriate telephone lines by traversing the table of pointers.
This prior art technique is inefficient and memory-intensive. For instance, a 155 Mb/s SDH-like data stream having ATM and TDM cells could have 2,340 DSO bytes. Storing this many data bytes in the memory to extract a relatively few TDM bytes is highly inefficient and memory-intensive.
Consequently, there is a need in the art for method and apparatus that efficiently demultiplex signals for different applications from a signal stream. There is also a need for method and apparatus that efficiently multiplex signals for different applications into a signal stream. More generally, there is a need for method and apparatus that identify signals for a set of communication devices in a signal stream which has signals for a number of different sets of communication devices.